Articles made from expanded polystyrene and similar foams are produced from a starting material in the form of small pellets which are placed in a mould and heated whereupon gas is liberated within each pellet and it expands into a foam bead which adheres to its adjacent beads. The quantity of pellets inserted into the mould is calculated so that once each has expanded into a bead the resulting mass of beads adhered together fills the mould.
It sometimes happens, of course, that a faulty article is produced or for other reasons scrap material is produced and for economy it is desirable to reprocess such scrap material.
Conventionally, the reprocessing is achieved by fragmenting the scrap into particles and including a minor proportion of those particles within a mould with pellets for incorporation in a further article.
Hitherto the apparatus for reclaiming scrap foam has comprised conventional type pulverisers or mills utilizing rapidly rotating hammers or blades to fragment the scrap by impact or utilizing cooperating toothed milling plates which disintegrate the scrap by a shearing action between pairs of closely spaced teeth.
Typical of prior art devices are those described in specification of U.S. Pat. No. 3,815,835 Australian Pat. No. 19579/34 and Australian Pat. No. 164,887.
Such prior known devices are noisy, use large amounts of power and usually have small intake apertures reducing their effective throughputs for low density but bulky scrap such as plastics foam.
Furthermore due to the fragmenting or grinding action much of the foamed material is crushed with consequent release of gases from within its cells. The reclamation action is usually not completed in a single pass through the device and some material may remain therein for a period before being reduced to the required size. This further damages the particles and also creates a considerable amount of dust.
As a result the granulate produced by previously known apparatus is not homogeneous, the particles are irregular in shape and thus neither flow freely nor mix readily with freshly formed beads in a subsequent moulding process.
Therefore freshly moulded material incorporating prior known reclaimed foam granulate is frequently uneven in composition and dust accumulations are visible in it. The crushed particles tend to shrink into solid lumps in the foam mass and if, for example, the article being produced is a block of foam intended subsequently to be cut to shape the wire cutting elements commonly used for that purpose on striking such hard lumps deflect and leave flaws in the cut surface.